A source told us Santos and Costa had been living together in LA when she decided to move to New York last August to pursue modeling. She met Marsden in the city in the fall, and the two started dating.

“Santos found out and flew to New York to win her back,” a source told us, adding the couple then reunited and moved back to LA. “They spent the holidays together and got a new apartment.”

But a few months later, Costa needed to renew her visa and flew back to Brazil with a two-day layover in Miami. Marsden was in Miami at the same time, and the two spent the night together.

We are told that when Costa came home, Santos confronted her about Marsden. “She confessed everything. She told him they hooked up one night, one time,” a source told us, adding they split and Costa immediately moved out. Another source insists she and Santos had gone their separate ways before she got together with Marsden.

A month later, Santos contacted Costa, who confessed she’s expecting Marsden’s baby. We’re told she’s now three months pregnant and is planning on keeping the child.

Reps for Santos and Costa had no comment. A rep for Marsden didn’t get back to us.